2012 Prius v Eco mode or not....

One thing I've noticed (or believe that I've noticed) is that with Eco mode you really still need to Pulse & Glide, in that the resolution of the throttle pedal is so focused on the low end that it takes seeming dramatic adjustments to move from ICE to electric drive on stretches of road where one might basically be coasting.

In Normal mode an equal foot-action would more easily trigger the electric drive; I often used pulse-and-glide in my past life owning an ICE-only machine.

I like the foot positioning and encouragement to take it easy in "ECO" mode, but other than some very limited control of the HVAC, the modes really only correspond to throttle maps.

Some others have noticed they get better fuel economy in Power mode of all things, so it really comes down to driving style and preference more than anything.

 

Getting to cruising speed as fast as possible and then pressing on the gas to maintain speed maximizes fuel economy. It's documented in the owners manual. In effect, ragging on the car gives you better fuel economy.

Being gentle on the gas only forces more EV use. Since the battery is charged by regenerative brakes, the energy captured sources from gasoline. It's not a 100% conversion, so forcing EV use by being gentle on the gas is worse for fuel economy.

I would redo your experiment in ECO mode. This time speed up as fast as you can without going into the PWR region of the HSI. I think you will find further improvement in your fuel economy.

iPhone ?

 

This is not a statistically significant variation. IOW, you could get that variation every day regardless of the mode you drive in. So, nothing gives. Over many tanks of fuel you might see differences between ECO and normal modes, but it really depends on conditions and your driving technique. There are way too many variables to give just the one variable too much credit for differences.

 

In MS, in the summer, I can tell the difference both on the gas gauge and by how long it takes to cool the cabin. The rest of the year it is too subtle for me.

 

Rapid acceleration is going to result in much lower mileage. You can see this pretty clearly using the AVG gauge on a ScanGauge. The average mileage goes down very rapidly as you accelerate more aggressively. I am not familiar with the ragging technique, but I have found that pulse and glide is the best way to good mileage. Using the energy in the battery during the glide uses the battery energy most efficiently. Contrary to what is often posted here, the regenerated battery energy has no energy cost associated with it, and by using it you can maximize your mileage. The engine will also charge the battery, but even in this case, the Synergy firmware is continually altering the charging rate to maximize efficiency. You can monitor this using an OBD device that will watch the battery charge/discharge rates.

 

Yes "regenerated battery energy" is free. But, not all battery energy is from regeneration.

Most people who try to "baby" the car up to speed by not using the ICE are using a counter productive method.

 

Instantaneous fuel economy goes down rapidly by accelerating aggressively not necessarily average fuel economy.This is why Pulse and Glide works. The ICE is less efficient when it is on. The faster you get up to speed, the less time you spend in Pulse and the more time you spend in Glide where the ICE is off.

It is a fallacy that the energy from the battery is free. Gasoline energy brought the car up to speed in order to regenerate that energy from the brakes. Gasoline energy brought the car up the hill in order to allow gravity to regenerate energy from the brakes. And obviously gasoline is used by the ICE to directly charge the battery. I think we've already had this conversation before and you are not convinced. Until you realize that energy cannot be created in the battery for free we'll just have to disagree.

 

Explain this then:

You accelerate to 35mph, then, by regen braking, slow to a stop. Repeat exactly, but put the car in N and use the hydraulic brakes. You have used exactly the same amount of gasoline each time, but in the first case you have reclaimed some energy into the battery. Where is the cost? There isn't any. The gasoline accelerates the car, but it does not know what happens next. The regen system also doesn't know how the car got up to speed. Yes, I noted that the engine will also charge the battery. And no, I do not think that energy gets created in the battery. Pulse and glide is the most efficient when you accelerate to just beyond the midpoint on the system indicator, which takes you out of EV and gets the engine running. By using a ScanGauge, you can find this out for yourself.

 

There is a cost as you accelerated more than required if you had to brake at the other end. You are capturing some of that extra energy you expended, but not all (probably a fairly low efficiency rate). Realistically you would probably never exactly accelerate enough to come to a rolling stop at the other end (and would frustrate any other cars behind you in the process), but the assumption that the regenerative braking energy is free is false.

Similarly with a hill. The regen energy captured going down hill is not free as you had to expend energy to get up the hill in the first place. Yes it's better than purely using brakes, but it's better to avoid the hill altogether.

 

In both cases the energy cost originated from gasoline. In the first case, the energy is reclaimed into the battery. In the second case, the energy is expended in heat and brake dust. The first case is more efficient because you will be reusing that energy in the future.

Imagine a third case where you don't accelerate to 35 mph but just enough to cover the same distance as the 1st two cases and you glide allowing friction to stop the car. You accelerate just enough to take you the distance you need. Which is more fuel efficient? That's the argument here. Case 3 is most fuel efficient and no energy is regenerated at all.

 

Your statement was that there was a cost to the battery regenerated energy. Obviously, the energy is wasted during hydraulic braking. I think that is the point. You are using the same amount of gasoline energy in both cases, but end up with some energy in the battery in one and wasted heat in another. Your third case may be the most efficient. I am not convinced, but in any case, it is not a practical driving system. There have been many discussions over the years about this kind of thought experiment. There are a lot of factors to look at such as the car continuing to use energy during the extra time it takes to glide to a stop. There may be a way to regen slowly to supply the car which is more efficient yet.